Efficient imposition of arbitrary postscript® files without preprocessing by defining a virtual device that specifies a desired position of a page on an output device while redefining postscript save and restore operators

Abstract

In a method of imposing selected pages defined in a sequence of page descriptions included in a PostScript® file, the selected pages are interpreted by an interpreter and may be transmitted to a raster memory for rendering on a flat by an output device. If the current page is a selected page to be rendered on the flat, a virtual device is defined as the output device for the selected page such that the virtual device specifies an area in a raster memory for positioning the selected page on the flat, and the selected page is interpreted. If the current page is not a selected page, a next page is determined as a selected page to be rendered on the flat, the virtual device is defined for the next selected page as the output device for the non-selected page, and the non-selected page is interpreted. A PostScript® save operator is redefined in order to save a definition of the virtual device. A PostScript® restore operator is redefined in order to apply an accumulation of operations applied on the saved definition of the virtual device to a current virtual device.

I claim: 
     
       1. A method of imposing selected pages defined in a sequence of page descriptions included in a PostScript® file, wherein the selected pages are interpreted by an interpreter and may be transmitted to a raster memory for rendering on a flat by an output device, comprising the steps of: a) determining whether a current page from the sequence of page descriptions is a selected page to be rendered on the flat;   b) if the current page is a selected page, i) defining a virtual device as the output device for the selected page, wherein the virtual device specifies an area in the raster memory for positioning the selected page on the flat; and   ii) interpreting the selected page     c) if the current page is not a selected page, i) determining a next page in the sequence of page descriptions that is a selected page to be rendered on the flat;   ii) defining the virtual device for the next selected page as the output device for the non-selected page; and   iii) interpreting the non-selected page;     d) redefining a PostScript® save operator to save a definition of the virtual device; and   e) redefining a PostScript® restore operator to apply an accumulation of operations applied on the saved definition of the virtual device to a current virtual device.   
     
     
       2. The method of claim 1, further comprising a step (b) (iii) of transmitting the interpreted page from the raster memory to the output device for rendering on the flat. 
     
     
       3. The method of claim 1, wherein the steps (b) (i) and (c) (ii) of defining the virtual device further comprise the steps of: A) defining a width and height of the virtual device as a page width and a page height of the selected page;   B) defining a matrix specifying a coordinate system of the selected page to position the selected page on the flat; and   C) defining a clipping path as a border of the area in the raster memory for positioning the selected page.   
     
     
       4. The method of claim 3, wherein step (d) of redefining the PostScript® save operator comprises appending the width and height of the virtual device to a current path. 
     
     
       5. The method of claim 4, wherein step (d) of redefining the PostScript® save operator further comprises appending components of the matrix specifying the coordinate system of the virtual device to the current path. 
     
     
       6. The method of claim 5, wherein step (e) of redefining the PostScript® restore operator comprises retrieving the width and height of the virtual device from the current path. 
     
     
       7. The method of claim 6, wherein step (e) of redefining the PostScript® restore operator further comprises retrieving the components of the matrix specifying the coordinate system of the virtual device from the current path. 
     
     
       8. The method of claim 1, wherein step (e) of redefining the PostScript® restore operator further comprises the steps of: W) determining a page orientation of a restored virtual device;   X) determining a page orientation of a current page to be interpreted;   Y) comparing the page orientation of the restored virtual device to the page orientation of the current page; and   Z) if the page orientation of the restored virtual device is different from the page orientation of the current page, changing the page orientation of the current page to be the same as the orientation of the restored virtual device.   
     
     
       9. The method of claim 8, wherein changing the page orientation of step (Z) comprises the steps of: i) specifying corner coordinates of the current page in the changed page orientation;   ii) translating an origin of the current page; and   iii) rotating the current page about the origin.